On Sunday 21 September 2003 15:00, Dean Anderson wrote: > It never sends the email in either case. In the first case, it will say no > such host, and return an error to the user. In the second case, it will > attempt to connect to 64.94.110.11 and will get an error, which will be > returned to the MUA. > > In both cases, it is permissible for the MTA to try again later in the > first case. > > Both of these are perfectly valid responses. You get them at the same > time, or you get the second one sooner. Not quite totally true. In the second case - it _will_ connect and initiate the transfer (helo, mail from, rcpt to) phase of _sending_ the message. It will fail, but it will make the attempt. Whereas with the first case it will never try. The second is much, much slower from the perspective of a mail server. -- Larry Smith SysAd ECSIS.NET sysad@ecsis.net